The present invention relates to prosthetic devices for replacing worn articular cartilage and restoring space between bones in a joint.
The knee joint is the union between the femur and the tibia. The knee joint, generally, is formed of a pair of condyles (medial and lateral) located at the distal portion of the femur and a tibial plateau located at the proximal end of the tibia and shaped to mate with the pair of condyles. The knee joint is considered a bi-compartmental joint having a medial compartment, which is defined by the medial condyle and its mating portion of the tibial plateau, and a lateral compartment, which is defined by the lateral condyle and its mating portion of the tibial plateau. A healthy knee joint includes a well-proportioned amount of articular cartilage between the articulating surfaces of the condyles and tibial plateau in each compartment. This cartilage, often referred to as the medial meniscus and lateral meniscus, serves as a cushion between the articulating surfaces of the femoral condyles and the tibial plateau.
Osteoarthritis is a common form of arthritis occurring in the joint and brought about by trauma to the joint, genetic predisposition, and/or aging. Osteoarthritis is characterized by a progressive deterioration and loss of the articular cartilage in the joint. In the case of osteoarthritis in the knee, the degeneration of the articular cartilage in the two compartments of the knee is often uneven resulting in an ill-proportioned amount of cartilage in the compartments. In other words, one compartment of the knee may be left with significantly less articular cartilage. The absence of sufficient cartilage in a compartment leaves the patient lacking proper cushion and spacing between the bones in that compartment. Ultimately, this may cause the femur to tilt downward toward the more heavily-eroded compartment, thereby resulting in a varus or valgus presentation of the knee. As a further consequence, either of these presentations may place added pressure on the already deteriorated cartilage thereby exacerbating and, perhaps, accelerating further degeneration of the articular cartilage remaining in the compartment. Practically, the lack of proper cushioning between the articulating surfaces of the femur and tibia can cause the patient remarkable pain and discomfort.
Attempts have been made to treat this condition by replacing the articulating surfaces via a total or uni-condylar knee replacement. Although successful, these methods may be significantly invasive and may require the removal of a significant amount of bone structure. Alternatively, prosthetic spacers have been proposed that may be implanted in a single compartment of the knee to restore the proper spacing. These prosthetic spacers are often called “uni-spacers.” Uni-spacers are typically rigid constructs formed of metal, such as cobalt chrome.
There is a need for a joint spacer that can be implanted into a joint to replace worn articular cartilage, restore joint spacing, and alleviate pain without the need for significant bone remodeling.